1. Field of the Invention
The invention relates to a system for recording and/or reproducing information, comprising a magnetic tape formatted with the aid of a magnetic write head, said magnetic tape being movable in a longitudinal direction (x) with respect to said magnetic write head, and including an apparatus having a magnetic read/write head having magnetic read/write units for writing data tracks into a magnetic tape movable in a longitudinal direction (x) with respect thereto, said read/write head being movable in a width direction (y) with respect to the longitudinal direction (x) of the magnetic tape by means of an actuator, the magnetic tape being previously provided with a pattern of buried servo tracks (STn) by the write head, said buried servo tracks extending in the longitudinal direction (x) and alternately containing a different servo signal, said buried servo tracks including at least one group of juxtaposed servo tracks of a width (w1), and at least one servo track of greater width, said apparatus further including control means for controlling the actuator by means of a control signal, said control means receiving servo read signals originating from servo signals embedded in adjacent servo tracks and read by the read/write units of said magnetic read/write head, and processing said servo read signals in a processing unit so as to form said control signal for the actuator, to a magnetic write head, to a magnetic tape provided with a pattern of buried servo tracks, comprising buried servo tracks of a first type containing a first servo signal (Sa), and buried servo tracks of a second type containing a second servo signal (Sb), said servo tracks extending substantially in a longitudinal direction (x), and said track pattern, in a transverse direction (y) perpendicular to the longitudinal direction (x), alternately comprising a servo track of the first type and a servo track of the second type, at least one group of servo tracks having a width w1 and at least one servo track having a greater width, said magnetic tape being able to cooperate with a magnetic read/write head of a given type is movable by an actuator in a width direction (y) with respect to the longitudinal direction (x) of the magnetic tape, as well as to an arrangement for formatting a magnetic tape including a magnetic write head and means for scanning a magnetic tape by means of the magnetic write head, in which the write head has a head face having a longitudinal direction (x) which corresponds to the longitudinal direction of movement of a magnetic tape with respect to the write head, and a width direction (y) which is perpendicular to the longitudinal direction and extends parallel to a generatrix of the head face, a structure of integrated write units has been provided in the write head, the write units being juxtaposed and extending in the width direction (y), and each of the write units having at least one write gap terminating in the head face and having a dimension in the width direction, said dimension corresponding to the width of the corresponding servo track, and at least one group of juxtaposed write units of a width w1 being provided and at least one write unit of greater width being provided.
2. Description of the Related Art
Such a system, such a magnetic write head, such a magnetic tape, such a cassette and such an arrangement are known from International Patent Application No. WO 98/26410, corresponding to U.S. Pat. Nos. 5,912,778 and 6,061,196, the subject matter of which, insofar as it is relevant to the present Application, is incorporated in the present Application by reference. other publications which are of relevance to the present Application are International Patent Application Nos. WO 96/30897 (corresponding to U.S. Pat. Nos. 5,966,276 and 6,097,571), WO 97/17699, WO 97/19446 (corresponding to U.S. Pat. No. 5,933,290), WO 97/21213 (corresponding to U.S. Pat. No. 5,805,372), and WO 97/33274 (U.S. Pat. No. 5,982,591). All said publications, insofar as relevant hereto, are incorporated in the present description by reference.
The known system, the known magnetic tape, the known magnetic write head, the known cassette and the known arrangement, make it possible to position the magnetic read/write head with a high accuracy with respect to the pattern of data tracks on the magnetic tape. This enables information to be read from and written into the pattern of data tracks during the movement of the magnetic tape in the one direction and in the reverse other direction. The described system enables the information to be read from and written into the pattern of data tracks while the servo tracks are read and the magnetic read/write head is controlled on the basis of the scanned servo signals, as a result of which, the position signal is immune to tolerances in the width of the servo track. This immunity is obtained, inter alia, in that always at least two magnetic read/write units are situated on the boundary between two adjacent servo tracks, and in that these read/write units read a servo track of the same type by means of facing parts and read a servo track of the other type by means of parts which are remote from one another. The above-mentioned tolerances influence the signals read by these read/write units to the same degree, as a result of which, the tolerances in the actuator drive cancel one another because this drive is based on the difference between the signals read by the relevant read/write units.
It has been found that the format of the inscribed servo signals gives rise to unequal amplitudes of the signals read from the servo tracks having a width larger than the data tracks. This reduces the overall signal-to-noise ratio of the servo system and may lead to an undesired degree of limitation of the track density. The reason for this is that the read/write units of the read/write head appear to be sensitive not only to the parts of the servo tracks situated directly beneath the active part of the read/write units, but also to those parts of the servo tracks which extend adjacent the active party of the read/write units. As a consequence, the servo tracks of larger width are read with a greater amplitude than the other servo tracks. This has a negative effect on the servo control of the read/write head. A reason for this is that the asymmetry of the servo signal thus read causes a reduction of the accuracy of the analog/digital conversion of the servo signal read.
It is an object of the invention to provide a system as described above, which does not have said drawbacks. The system in accordance with the invention, is characterized in that the amplitude of the servo read signal as a function of the position of the magnetic read/write head of the apparatus with respect to the magnetic tape in the width direction (y) is substantially equal for all the read/write units of the read/write head. The aforementioned undesired reduction of the signal-to-noise ratio of the servo system is avoided in that the amplitude of the servo read signals as a function of the position of a magnetic read/write head of the apparatus is substantially constant.
In one embodiment of the invention, care is taken that the servo tracks of greater width induce a signal into the relevant read/write units with an amplitude which is the same as that of the servo signals for the other read/write units.
In a preferred embodiment of the present invention, the servo signals in the embedded servo tracks of greater width are given a suitable effective value by dividing the servo track into a plurality of signal-carrying sub-tracks alternating with one or more empty sub-tracks.
A magnetic write head, in accordance with the invention, is adapted to format magnetic tapes which are suitable for the system described above, which has signal-carrying sub-tracks and or more empty sub-tracks.
In an embodiment of write heads according to the invention, the write heads can be manufactured with the aid of a so-called thin-film technology.
The magnetic tape in accordance with the invention has been pre-formatted in such a manner that during cooperation with a magnetic read/write head of the system, the servo read signals obtained from the various servo tracks, including those from the broader servo tracks, have substantially equal amplitudes.
This can be achieved, for example, by recording a servo signal of smaller amplitude in the broader servo tracks. It is also possible to use a magnetic tape where the servo tracks of greater width have been divided into one or more signal-carrying tracks and one or more empty servo tracks.
In a further embodiment of the invention, the magnetic tape can be accommodated in a cassette.
A further embodiment of the invention offers an arrangement for formatting a magnetic tape for use in the system in accordance with the invention, which utilizes a magnetic write head in the preferred embodiment mentioned hereinbefore for writing a sub-set of tracks comprising one or more signal-carrying sub-tracks and one or more empty sub-tracks.